A service provider network typically comprises a number of different types of computer networks interconnected to one another. One type of network referred to as an access network enables subscriber devices, which may also be referred to as customer premises equipment (CPE), to access the service provider network. Subscriber devices or CPE may comprise set-top boxes (STBs), laptop computers, desktop computers, mobile devices (such as mobile cellular phones and so-called “smart phones”), Voice over Internet Protocol (VoIP) telephones, workstations, modems, wireless access points (WAPs), and other devices capable of accessing or otherwise facilitating access to the service provider network.
The access network typically comprises a number of access nodes, such as a Digital Line Subscriber Line Access Multiplexers (DSLAMs) or a Cable Modem Termination System (CMTS), that each manages access by one or more of the subscriber devices to the service provider network. The access node may, for example, multiplex traffic from subscriber devices into a composite signal and transmit this signal upstream to the subscriber network for delivery to one or more destinations. The access nodes may also manage multicast communications or streams to more efficiently utilize bandwidth of the access network between the access nodes and the subscriber devices.
For example, an access node may implement a multicast management protocol, such as an Internet Group Management Protocol (IGMP). IGMP provides a way to track subscriber device memberships in multicast groups. The subscriber devices may issue an IGMP join request to indicate to the access node that it has joined a multicast group. The access node may maintain a multicast group membership table that includes an entry for each multicast group currently subscribed to by at least one subscriber device. In response to the IGMP join request, the access node may update an entry in this table associated with the indicated multicast group to reflect the new membership by the subscriber device.
Likewise, the subscriber device may issue an IGMP leave request, indicating that the subscriber device has left a multicast group. The access node, in response to this leave request, may update the group membership table to reflect that the subscriber devices left the indicated group. Based on this table, the access node may determine whether one or more groups stored in the table is currently being subscribed to by more than one subscriber device. If no subscriber devices are subscribing to a particular multicast group, the access node may stop streaming or otherwise delivering the multicast content from this group to the subscriber devices, thereby more efficiently utilizing the bandwidth in the access network.
However, IGMP leave requests may be lost or corrupted before arriving at the access node, which may prevent access nodes from successfully determining whether or not any of the subscriber devices are still active members in the one or more multicast groups. This may result in bandwidth inefficiencies, as the access node may continue to deliver multicast streams even though none of the subscriber devices are members of the corresponding multicast group. To overcome this inefficiency, the access node may periodically issue an IGMP general query to the subscriber devices, which may respond with an IGMP report detailing the one or more multicast groups to which each of the subscriber devices is currently a member. Based on these reports, the access node may determine whether to continue streaming the multicast content for all or a subset of the groups listed in the multicast group membership table. In this manner, IGMP provides a failsafe to overcome bandwidth inefficiencies resulting from lost or corrupted IGMP leave requests.